Installation of laser vent holes into vertical walls of cavity-back airfoils

ABSTRACT

A method of manufacturing an airfoil includes creating a plurality of cavities separated by a plurality of internal ribs in an airfoil forging. At least one hole is drilled in at least one of the plurality of internal ribs with a laser drilling tool. At least one hole extends perpendicularly to a wall of the rib.

BACKGROUND

This disclosure relates to gas turbine engines and more particularly toan improved hollow fan blade for a gas turbine engine and method andtool for making the same.

A gas turbine engine typically includes a fan section, a compressorsection, a combustor section, and a turbine section. Air entering thecompressor section is compressed and delivered into the combustionsection where it is mixed with fuel and ignited to generate ahigh-temperature and pressure gas flow. The hot gas flow expands throughthe turbine section to drive the compressor and the fan section. The fansection includes a rotor assembly and a stator assembly. The rotorassembly of the fan includes a rotor disc and plurality of radiallyextending fan blades. Fan blades are used to direct air into the engine,and typically have an airfoil shape that includes a twist from the rootof the blade to the tip of the blade.

In order to reduce weight, the fan blades in some gas turbine enginesare hollow. Historically, each fan blade is made by combining twoseparate detail halves. Each half may include a plurality of cavitiesand ribs machined out to reduce the weight. These halves aresubsequently bonded together to form the hollow fan blade. The hollowfan blade is then subjected to forming operations at extremely hightemperatures at which time it is given an airfoil shape and geometry.During the forming operation, the two halves are twisted and camberedunder high temperatures to the desired shape. This process for producinga hollow fan blade can be time-consuming and expensive. The processdescribed hereafter pertains to a lower cost and simplified method ofproducing a hollow fan blade.

SUMMARY

In one exemplary embodiment, a method of manufacturing an airfoilincludes creating a plurality of cavities separated by a plurality ofinternal ribs in an airfoil forging. At least one hole is drilled in atleast one of the plurality of internal ribs with a laser drilling tool.At least one hole extends perpendicularly to a wall of the rib.

In a further embodiment of the above, a cover is joined to the forgingto form a complete airfoil.

In a further embodiment of any of the above, the joining comprises laseror electron beam welding around a periphery of the forging and along atleast one of the internal ribs.

In a further embodiment of any of the above, a root hole is drilled in aroot portion of the airfoil forging before the joining of the cover. Theroot hole is sealed before the airfoil is used in service.

In a further embodiment of any of the above, a protective fixture isinserted into one of the plurality of cavities opposite an internal ribfrom the drilling tool before the drilling of at least one hole.

In a further embodiment of any of the above, the protective fixture ismetallic or ceramic.

In a further embodiment of any of the above, at least one hole isdrilled at a midpoint of the internal rib between a floor of the forgingand a top edge of the rib.

In a further embodiment of any of the above, at least one hole has adiameter of less than about 3/32 of an inch.

In a further embodiment of any of the above, the drilling is automatedusing a robotic controller.

In a further embodiment of any of the above, the airfoil forging is atitanium alloy.

In a further embodiment of any of the above, the airfoil is a fan bladefor a gas turbine engine.

In a further embodiment of any of the above, the plurality of internalribs comprises a plurality of circular ribs and a plurality of linearribs that connect the circular ribs. The plurality of circular ribs havea greater height than a height of the linear ribs.

In another exemplary embodiment, a tool for machining an airfoilincludes an elongated tool body that has a top end, a bottom end, and asidewall that extends between the top end and the bottom end. A laser isconfigured to provide a laser beam from the top end to near the bottomend. A reflector is arranged near the bottom end and is configured toturn the laser beam at a right angle such that the laser beam exits thetool body through an aperture on the sidewall near the bottom end.

In a further embodiment of any of the above, a rubber bumper is at thebottom end and is configured to abut a work piece during use.

In a further embodiment of any of the above, a robotic controller isconfigured to automatically operate the tool.

In a further embodiment of any of the above, a protective fixture iscontrolled by the robotic controller. The protective fixture isconfigured to be positioned on an opposite side of a wall to be drilledfrom the tool body.

In a further embodiment of any of the above, the tool body iscylindrical and has a diameter of less than about one inch.

In a further embodiment of any of the above, the aperture is in thesidewall less than about 0.5 inches from the bottom end.

In a further embodiment of any of the above, the aperture is about 0.25inches from the bottom end.

In another exemplary embodiment, an airfoil includes an airfoil bodythat has a tip end and a root end. A first side extends between the tipend and the root end. A plurality of internal ribs extend from the firstside and form a plurality of internal cavities. A hole extends throughat least one of the internal ribs in a direction parallel to the firstside. A cover laser is welded to at least one of the plurality ofinternal ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings.

FIG. 1 is a schematic view of an example gas turbine engine according toa first non-limiting example.

FIG. 2 is a view of a fan blade having a machined forging as an airfoilbody.

FIG. 3 is a view of the fan blade having a machined forging as anairfoil body of FIG. 2 without a cover.

FIG. 4 is another example of a fan blade having a forging as an airfoilbody.

FIG. 5 shows a sectional view along line 5-5 of the fan blade of FIG. 2.

FIG. 6 schematically illustrates an exemplary tool for manufacturing anairfoil.

FIG. 7 schematically illustrates a method for manufacturing an airfoil.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct defined within a nacelle15, and also drives air along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a two-spool turbofan gasturbine engine in the disclosed non-limiting embodiment, it should beunderstood that the concepts described herein are not limited to usewith two-spool turbofans as the teachings may be applied to other typesof turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects, a first (or low) pressure compressor 44 and a first (orlow) pressure turbine 46. The inner shaft 40 is connected to the fan 42through a speed change mechanism, which in exemplary gas turbine engine20 is illustrated as a geared architecture 48 to drive a fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a second (or high)pressure compressor 52 and a second (or high) pressure turbine 54. Acombustor 56 is arranged in the exemplary gas turbine engine 20 betweenthe high pressure compressor 52 and the high pressure turbine 54. Amid-turbine frame 57 of the engine static structure 36 may be arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 57 further supports bearing systems 38in the turbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of the low pressure compressor, or aftof the combustor section 26 or even aft of turbine section 28, and fan42 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. The low pressure turbine 46 pressure ratio is pressuremeasured prior to the inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1 and less than about 5:1. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and35,000 ft (10,668 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Lowcorrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second (350.5meters/second).

The fan section 22 comprises a fan case containing a rotor assembly. Therotor assembly includes a rotor disk and a plurality of fan blades. Eachfan blade extends radially outwardly from the rotor disk into proximitywith the fan case. The fan blades are hollow fan blades having aplurality of pockets. These hollow fan blades may be constructed in twohalves. The pockets in the fan blades remove a significant amount ofmaterial from the fan blade, which decreases the weight of the fansection 22. A blade skin or cover is attached to the fan blade to sealthe pockets. Details of the hollow fan blade and a method and tool formanufacturing are set forth more fully herein.

FIG. 2 is a view of a fan blade 60 having a forging as an airfoil body62. The airfoil body 62 has a root end 64 and a tip end 66. The airfoilbody 62 has a twisted airfoil shape. In some embodiments, the airfoilbody 62 may twist about 60 degrees from the root end 64 to the tip end66. The thickness of the airfoil body 62 may vary, with the thickestportion being at the root end 64. The airfoil body 62 has a first side68 that extends from the root end 64 to the tip end 66, and a secondside 70 that extends from the root end 64 to the tip end 66. The airfoilbody 62 may include a cover 72 attached to the first side 68 by laser orelectron beam welding.

The cover 72 is very thin, and may be superplastic formed from a flatpiece of titanium sheet metal. In one embodiment, the cover 72 may bebetween about 0.040 inches and about 0.080 inches. The cover 72 isattached to the fan blade 60 such that an exterior surface of the cover72 is about flush with the exterior surface of the first side 68. Thecover 72 is attached to the airfoil body 62 by laser or electron beamwelding at its periphery and/or through the cover 72. Details of thewelding of the cover are found in co-pending U.S. patent applicationSer. No. 15/670,654, entitled “Power Beam Welded Cavity-Back TitaniumHollow Fan Blade,” filed on Aug. 7, 2017, the entirety of which isherein incorporated by reference.

FIG. 3 is a view of the twisted airfoil body 62 with cavities machined,but without the cover 72. In order to reduce weight while stillmaintaining the necessary stiffness and strength, a plurality ofcavities 74 are machined into the interior surface of the airfoil body62. The cavities 74 form a plurality of intersecting ribs 76. The ribs76 are oriented in order to provide stiffness where needed during use ofthe engine 20. In one embodiment, the ribs 76 have a generally constantwidth. The ribs 76 help carry the load on the fan blade 60. In theillustrated embodiment, several of the cavities 74 are circular cavities78. The ribs 76 surrounding the circular cavities 78 are circular ribs79, and the ribs 76 connecting the circular ribs 79 to each other or tothe periphery 81 of the airfoil body 62 are linear ribs 75. Although acircular rib configuration is illustrated, this disclosure may extend toother cavity configurations, such as rectangular cavities.

The cavities 74 are fluidly connected via a crossover hole 80. The hole80 is drilled in the rib 76. In some embodiments, a crossover hole 80connects each of the cavities 74. In another embodiment, each circularrib 79 has a crossover hole 80. Each of the cavities 74 are fluidlyconnected such that gases can travel between the cavities 74 and outthrough the root end 64 at a root hole 82.

In some embodiments, the circular ribs 79 have a different height d2than a height d1 of the linear ribs 75 (shown in FIG. 5). For example,the circular ribs 79 have a greater height d2 than the height d1 of thelinear ribs 75. In these embodiments, only the circular ribs 79 need ahole 80. When the cover 72 is attached, it will abut the taller circularribs 79, leaving a gap between the cover 72 and the shorter linear ribs75. Thus, gas will be able to travel between adjacent cavities 74 in thespace between the cover 72 and the linear ribs 75. In such aconfiguration, only a single crossover hole 80 is needed on eachcircular rib 79, to allow for gas communication between all of thecavities 74 and the root hole 82.

In one example, the cover 72 is attached to the airfoil body 62 by laseror electron beam welding around the periphery 81 of the airfoil body 62.In another example, the cover 72 is attached to the airfoil body 62 bylaser or electron beam welding through the cover 72 and onto the ribs76. In a further example, the cover 72 is attached to the airfoil body62 by welding around the periphery 81 of the airfoil body 62 and alongthe circular ribs 79. Welding around both the periphery 81 and thecircular ribs 79, rather than just around the periphery 81, may provideimproved fatigue characteristics for the fan blade 60. Welding aroundthe circular ribs 79, rather than along a linear rib, may provide a moreconsistent weld, because a circular weld may have fewer defects at thestart and end of the weld because it provides an opportunity to go backover the starting point.

The welding of the cover 72 to the airfoil body 62 is done in an Argonenvironment to help prevent contamination. However, when the airfoilbody 62 is heated, the Argon expands. Crossover holes 80 are machinedinto the ribs 76 before the welding. In one embodiment, the crossoverholes 80 have a diameter of less than about 0.0625 inches. In a furtherembodiment, the crossover holes 80 have a diameter between about 1/32and 3/32 inches. These crossover holes 80 give the Argon a place to gowhen it expands at high temperatures. In other embodiments, the weldingof the cover 72 may be done in a vacuum. In this example, when theairfoil body 62 is heated, the cavities 74 may collapse. The crossoverholes 80 allow gas to flow into the cavities to equalize the pressure athigh temperatures.

In an embodiment, there is one crossover hole 80 drilled into each ofthe circular ribs 79 and a root hole 82 located near the root end 64.The root hole 82 allows pressure inside the airfoil body 62 to equalizeduring a heat treat cycle by allowing gas to exit the fan blade 60through the root. Each cavity 74 is thus in gas communication with anadjacent cavity, and one cavity is in communication with a root of theblade 60. This pressure equalizing helps prevent bulging of the internalcavities at high temperatures due to gas expansion.

FIG. 4 illustrates another example airfoil body 162. In this disclosure,like reference numerals designate like elements where appropriate andreference numerals with the addition of one-hundred or multiples thereofdesignate modified elements that are understood to incorporate the samefeatures and benefits of the corresponding original elements. In thisembodiment, several cavities 174 in the lower half of the airfoil body162 near the root end 64 are larger cavities. All of the circularcavities 176 in the upper half of the airfoil body 162 near the tip end166 are the same size. This embodiment may have the same configurationof crossover holes in each circular rib.

FIG. 5 illustrates a cross-sectional view along line 5-5 of FIG. 3. Theairfoil body 62 is machined from a twisted fan blade forging 83 to havecavities 74 and ribs 76. In one non-limiting example, the forging 83 isabout 30 inches long by about 12 inches wide and may have a mid-chordthickness T of about 1 inch. The forging 83 may be a titanium alloy, forexample.

The cavities 74 are machined by removing material from the forging 83.The cavities 74 may be formed by milling, for example. This removing ofmaterial to form the cavities 74 also forms the ribs 76. Each rib 76 hasan upper end 84 and a lower end 86. Each cavity 74, 78 has a floor 88 atthe lower end 86 of the rib 76. The floor 88 extends between oppositewall interior surfaces 90, some of which define the ribs 76. Each cavity74, 78 further includes a radius transition 92 between the wall interiorsurface 90 and the floor 88. The cavities 74, 78 may extend from about ¼inch to about 1 inch to the floor 88. The floor 88 may have a thicknesst of about ⅛ inch thick. In a further embodiment, the floor 88 may beabout 60 thousandths of an inch thick. The floor 88 forms a thin outerwall of the airfoil 62. The circular cavities 78 may be about 1½ inchesin diameter. In some embodiments, the ribs 76 may be machined to havedifferent heights. In one example embodiment, the circular ribs 79 havea greater height d2 than the height d1 of the linear ribs 75.

Once a rib 76 is machined, a crossover hole 80 may be drilled in the rib76. The crossover holes 80 are drilled in the rib 76 at a height h fromthe floor 88. In one embodiment, the height h is about half of theheight d2 of the rib 76. In another embodiment, the crossover hole 80 isdrilled in the rib 76 near the floor 88. If the holes 80 are near a topsurface of the ribs 76, such as a notch in the rib, there may be a weakspot in the weld at that location once the cover 72 is attached. Theholes 80 may be drilled at a neutral axis of the blade 60, for example.In some embodiments, the interior surfaces of the cavities 74 include acoating that provides protection of adjacent surfaces when laserdrilling or laser or electron beam welding. In a further embodiment, thecoating is a polyimide or similar coating.

The crossover hole 80 is drilled such that it extends completely throughthe rib 76 to an adjoining cavity 74. The crossover hole 80 is parallelto a floor 88 of the forging 83, or perpendicular to the rib 76. Thisperpendicular orientation allows for the hole 80 to be located on aneutral axis of the blade 60. A perpendicular hole 80 further preventshigh stress concentrations at the sharp angles created by an angledhole. Such angled holes raise stress in the blade at that spot,particularly during fatigue conditions.

A tool 94 is used to drill the holes 80 into the ribs 76. The tool 94includes a tool body having a top end 91, a bottom end 106, and asidewall 93 extending between the top and bottom ends 91, 106. The tool94 may be a rod-shaped tool extending along a tool centerline 95. Knowndrills typically use drill bits, making it difficult to drill acrossover hole 80 that is perpendicular to the rib 76. The tool 94 usesa laser beam 96 directed at a 90 degree angle from the tool centerline95. This 90 degree turn of the laser beam 96 allows the tool 94 to beinserted into the cavity 78, and to drill a hole 80 that isperpendicular to the rib 76. A protective fixture 98 is positioned onthe opposite side of the rib 76 being drilled. The protective fixture 98acts as a stopper for the laser beam 96 to prevent the laser beam 96from drilling into other ribs 76 and to contain molten metallic spatter.

FIG. 6 illustrates a cross-sectional view of the tool 94. The tool 94includes a fiber optic laser 100 for supplying the laser beam 96 throughthe rod-shaped tool 94. A laser fiber 102 extends down the center of thetool 94. A reflector 104, such as a mirror or prism, resides near thebottom end 106 of the tool 94. The reflector 104 allows the laser beamto turn a sharp 90 degrees. The laser beam 96 strikes the reflector 104and is directed out through an aperture 108 to the rib 76 that is beingdrilled. The aperture 108 is located in the sidewall 93 near the bottomend 106. In some embodiments, the aperture is less than 0.5 inches fromthe bottom end 106. In a further embodiment, the aperture is about 0.25inches from the bottom end 106. In this embodiment, the hole 80 would bedrilled at a height h of about 0.25 inches from the floor 88. The tool94 further includes a bumper 110 at the bottom end 106. The bumper 110abuts the floor 88 when the tool 94 is inserted into a cavity 74, 78.The bumper 110 may be rubber, for example, and prevents the tool 94 fromscoring the floor 88. This prevents damage to the floor 88, which mayresult in stress concentrations in that area of the fan blade 60. Thetool 94 may be manufactured from a durable ceramic, such as siliconnitride, or from a wrought, cast, or additively manufactured,non-magnetic alloy.

The tool 94 is controlled by a controller 112, shown schematically. Inan embodiment, the controller 112 is a robotic controller using computernumerical control. The robotic controller 112 may be trained by imputingpositioning coordinates, the tool's rotational orientation about thecenterline 95, the power and time, and the sequence for drilling eachhole. Data may be loaded into the controller 112 such that either orboth the fixture 98 and tool 94 would be articulated to drill athrough-wall hole of proper diameter at a midpoint within each cavity'sadjacent wall. The controller 112 may be programmed to move the tool 94sequentially from one cavity to another to laser drill a crossover hole80 in each cavity's vertical rib 76. The controller 112 may beprogrammed such that it drills all of the crossover holes 80 in anairfoil body 62 in less than about 30 minutes. In a further embodiment,the controller 112 may be programmed to drill all of the crossover holes80 in an airfoil body 62 in between about 10 minutes and about 30minutes.

Concurrently with the tool's movement into position, the protectivefixture 98 would automatically move into position to provide a backstopfor preventing back strikes from occurring on an adjacent cavity'swalls. The protective fixture 98 helps prevent impingement of moltenmetallic spatter on the inside floor 88 of the cavity 74 or onto ribs76. In some embodiments, the protective fixture 98 has a circularcontour to allow it to be positioned close to a circular rib 79. Theprotective fixture 98 may include a recess positioned near the rib 79 tocatch material that is blasted through the hole 80 from the tool 94. Theprotective fixture 98 may be made of a metallic or ceramic material, forexample. The protective fixture 98 may be about 0.5 inches in width andabout 0.75 inches in height. The protective fixture 98 may also becontrolled by the controller 112. The controller 112 may be programmedto sequentially move the protective fixture 98 from one cavity to thenext along with the tool 94 to laser drill crossover holes 80 in eachcavity that needs one.

An example method of manufacturing an airfoil is summarized in theflowchart of FIG. 7. First, a plurality of cavities 74 and ribs 76 aremachined into a twisted airfoil forging 83 at step 114. In anembodiment, the forging 83 is a titanium alloy. Next, crossover holes 80are drilled into the ribs 76 at step 115. In an example embodiment, atleast some of the cavities 74 are circular cavities 78 surrounded bycircular ribs 79. The crossover holes 80 are drilled with a laser drilltool 94, such that the crossover holes 80 extend perpendicular to therib 76. These crossover holes 80 allow for gas communication betweenadjacent cavities 74. In an embodiment, a root hole 82 is also drillednear a root end 64 of the machined forging 83.

After the cavities 74 and ribs 76 are machined, and the crossover holes80 are drilled, a cover 72 is welded onto the machined forging 83 atstep 116. The welding 116 of the cover 72 to the airfoil body 62 may bedone using laser welding in an Argon environment to help preventcontamination.

After the cover 72 has been welded onto the airfoil body 62 at step 116,the fan blade 60 is stress relieved to reduce welding residual stressesat step 118. In some embodiments, the blade 60 goes through thermalprocessing with temperatures of up to about 1100 to 1600° F. Finally,the root hole 82 should be sealed before the airfoil 60 is used inservice.

The crossover holes 80 that were drilled at step 115 allow pressureneutralization during the thermal processing at step 118 by allowingexpanding gases, such as any Argon trapped in the cavities 74 from step116, to flow into adjacent cavities 74 and exit the blade 60 through theroot hole 82. This venting of the internal cavities through crossoverholes 80 prevents the Argon gas from bulging the sealed internalcavities during thermal processing. The disclosed tool and method mayallow titanium fan blades to be produced faster and at a lower cost.

It should also be understood that although a particular componentarrangement is disclosed in the illustrated embodiments, otherarrangements will benefit herefrom. Although particular step sequencesare shown, described, and claimed, it should be understood that stepsmay be performed in any order, separated or combined unless otherwiseindicated and will still benefit from the embodiments of the presentinvention.

Although the different examples have specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. A method of manufacturing an airfoil, comprising:creating a plurality of cavities separated by a plurality of internalribs in an airfoil forging; and drilling at least one hole in at leastone of the plurality of internal ribs with a laser drilling tool,wherein the at least one hole extends perpendicularly to a wall of therib; and joining a cover to the forging to form a complete airfoil,wherein the joining comprises laser or electron beam welding around aperiphery of the forging and along at least one of the internal ribs. 2.The method of claim 1, comprising: drilling a root hole in a rootportion of the airfoil forging before the joining of the cover; sealingthe root hole before the airfoil is used in service.
 3. The method ofclaim 2, comprising drilling a plurality of holes in the plurality ofribs such that each of the cavities is fluidly connected to the roothole.
 4. The method of claim 1, comprising: inserting a protectivefixture into one of the plurality of cavities opposite an internal ribfrom the drilling tool before the drilling of the at least one hole. 5.The method of claim 4, wherein the protective fixture is metallic orceramic.
 6. The method of claim 1, wherein the at least one hole isdrilled at a midpoint of the internal rib between a floor of the forgingand a top edge of the rib.
 7. The method of claim 1, wherein the atleast one hole has a diameter of less than 3/32 of an inch.
 8. Themethod of claim 7, wherein the diameter is greater than 1/32 of an inch.9. The method of claim 1, wherein the drilling is automated using arobotic controller.
 10. The method of claim 1, wherein the airfoilforging is a titanium alloy.
 11. The method of claim 1, wherein theairfoil is a fan blade for a gas turbine engine.
 12. The method of claim1, wherein at least some of the plurality of ribs are circular ribs. 13.The method of claim 1, wherein the plurality of ribs have a constantwidth.
 14. The method of claim 1, wherein the laser or electron beamwelding is done in an argon environment.
 15. The method of claim 1,wherein the laser or electron beam welding is done in a vacuum.
 16. Amethod of manufacturing an airfoil, comprising: creating a plurality ofcavities separated by a plurality of internal ribs in an airfoilforging; and drilling at least one hole in at least one of the pluralityof internal ribs with a laser drilling tool, wherein the at least onehole extends perpendicularly to a wall of the rib, wherein the pluralityof internal ribs comprises a plurality of circular ribs and a pluralityof linear ribs connecting the circular ribs, and wherein the pluralityof circular ribs have a greater height than a height of the linear ribs.